roomEnd property Null safety

1. netease_roomkit
2. netease_roomkit
3. NERoomEventCallback
4. roomEnd property

NERoomEventCallback class

1. Constructors
2. NERoomEventCallback
3. Properties
4. chatroomMessageAttachmentProgress
5. chatroomMessagesReceived
6. hashCode
7. liveStateChanged
8. memberAudioMuteChanged
9. memberJoinChatroom
10. memberJoinRoom
11. memberJoinRtcChannel
12. memberLeaveChatroom
13. memberLeaveRoom
14. memberLeaveRtcChannel
15. memberNameChanged
16. memberPropertiesChanged
17. memberPropertiesDeleted
18. memberRoleChanged
19. memberScreenShareStateChanged
20. memberVideoMuteChanged
21. memberWhiteboardShareStateChanged
22. roomEnd
23. roomLockStateChanged
24. roomPropertiesChanged
25. roomPropertiesDeleted
26. rtcAudioOutputDeviceChanged
27. rtcAudioVolumeIndication
28. rtcChannelError
29. rtcVirtualBackgroundSourceEnabled
30. runtimeType
31. whiteboardError
32. whiteboardShowFileChooser
33. Methods
34. noSuchMethod
35. toString
36. Operators
37. operator ==